Electrical Machines

Preface xv Acknowledgement xvii 1 Analysis of Electrical Power 1 1.1 Introduction 1 1.2 Power 1 1.3 Average Power and Reactive Power 5 1.4 Apparent Power 10 1.5 Complex Power 13 1.6 Complex Power Balance 20 1.7 Power Factor and Reactive Factor 24 1.8 Power Factor Correction 25 1.9 Three-Phase Voltage Generation 32 1.10 Phase Sequence 34 1.11 Wye Connection 35 1.12 Analysis of Wye Connection 36 1.13 Delta Connection 41 1.14 Analysis of Delta Connection 42 1.15 Analysis of Three-Phase Power 45 1.16 Basic Measurement Equipment 54 Exercise Problems 55 2 Magnetic Circuits 61 2.1 Introduction 61 2.2 Magnetic Force and Field 61 2.3 Magnetic Circuit 65 2.4 Magnetic Flux and Magnetic Flux Density 65 2.5 Magnetomotive Force 68 2.6 Magnetizing Force 69 2.7 Permeability and Relative Permeability 71 2.8 Reluctance 73 2.9 Permeance 75 2.10 Fleming’s Rules 77 2.11 Analogy of Magnetic and Electric Circuits 78 2.12 Ampere’s Circuital Law 79 2.13 Magnetic Flux Density of a Long Straight Wire 80 2.14 Toroidal Coil 82 2.15 Series Magnetic Circuit 84 2.16 Parallel Magnetic Circuit 88 2.17 Air Gap 92 2.18 Analysis of Magnetic Circuit with Air Gap 93 2.19 Electromagnetic Force on a Conductor 98 2.20 Force Between Two Parallel Conductors 103 2.21 Faraday’s Laws 104 2.22 Magnetic Materials and B-H Curve 105 2.23 Inductance and Mutual Inductance 108 2.24 Hysteresis Curve and Losses 114 Exercise Problems 117 3 Transformer 123 3.1 Introduction 123 3.2 Working Principle of Transformer 125 3.3 Transformer Flux 126 3.4 Construction of a Transformer 127 3.5 Ideal Transformer 128 3.6 E.M.F. Equation of Transformer 129 3.7 Turns Ratio of Transformer 131 3.8 Analysis of No-Load Phasor Diagram 136 3.9 Analysis of Load Phasor Diagram 138 3.10 Rules for Referring Impedance 138 3.11 Equivalent Circuit of a Transformer 142 3.12 Exact Equivalent Circuit 143 3.13 Approximate Equivalent Circuit 146 3.14 Polarity of a Transformer 149 3.15 Three-Phase Transformer 150 3.16 Transformer Vector Group 152 3.17 Voltage Regulation of a Transformer 160 3.18 Efficiency of a Transformer 165 3.19 Iron and Copper Losses 166 3.20 Maximum Efficiency 168 3.21 Transformer Tests 171 3.22 Autotransformer 177 3.23 Parallel Operation of a Single-Phase Transformer 181 3.24 Three-Phase Transformer Connections 186 3.25 Instrument Transformers 194 3.26 Transformer Oil Testing and Cooling 195 3.27 All-Day Efficiency of Transformer 197 Exercise Problems 199 4 Direct Current Generators 207 4.1 Introduction 207 4.2 Electromagnetic Induction 208 4.3 Motional Voltage 209 4.4 Lenz’s Law 212 4.5 Working Principle 213 4.6 Construction of a DC Generator 216 4.7 Armature Coils and Windings 217 4.8 Induced EMF of a DC Generator 221 4.9 Classification of a DC Generator 225 4.10 Separately Excited DC Generator 225 4.11 Self-Excited DC Generator 227 4.12 Series Generator 227 4.13 Shunt Generator 228 4.14 Compound Generator 231 4.15 Saturation Curve of a DC Generator 237 4.16 Generator Build-Up Process 241 4.17 Voltage Build-Up Failure Reasons 243 4.18 Field Circuit Resistance Lines 243 4.19 Theory of Commutation 244 4.20 Armature Reaction 246 4.21 Demagnetizing and Cross-Magnetizing 249 4.22 Cancellation of Armature Reaction 252 4.23 Series Generator Characteristics 254 4.24 Shunt Generator Characteristics 255 4.25 Compound Generator Characteristics 256 4.26 Applications of a DC Generator 258 4.27 Voltage Regulation of DC Generator 258 4.28 Losses of a DC Generator 260 4.29 Efficiency of a DC Generator 261 4.30 Parallel Operation of a DC Generator 265 Exercise Problems 267 5 Direct Current Motors 271 5.1 Introduction 271 5.2 Working Principle 272 5.3 Construction 273 5.4 Back EMF 274 5.5 Necessity of Back EMF 276 5.6 Classification of a DC Motor 276 5.7 Mechanical Power of a DC Motor 282 5.8 Torque of a DC Motor 286 5.9 Speed of a DC Motor 290 5.10 Speed Regulation of a DC Motor 294 5.11 Losses in a DC Motor 295 5.12 Efficiency of a DC Motor 297 5.13 Characteristics of a DC Motor 302 5.14 Characteristics of a Shunt Motor 302 5.15 Characteristics of a Series Motor 304 5.16 Characteristics of a Cumulative Compound Motor 307 5.17 Comparison Between Generator and Motor 309 5.18 Application of DC Motors 309 Exercise Problems 310 6 Control and Starting of DC Motors 315 6.1 Introduction 315 6.2 Speed Controlling Parameters 315 6.3 Flux Control Method 316 6.4 Armature Control Method 318 6.5 Armature Voltage Control Method 322 6.6 Speed Control of a Series Motor 323 6.7 Ward Leonard System 329 6.8 Semiconductor Devices 330 6.9 Half-Wave Rectifier 332 6.10 Full-Wave Rectifier 336 6.11 Speed Control by Thyristor and Diode 341 6.12 Braking of a DC Motor 344 6.13 DC Motor Starter 349 6.14 Three-Point Starter 349 6.15 Four-Point Starter 350 6.16 Grading of Starting Resistance 351 Exercise Problems 360 7 Three-Phase Induction Motor 365 7.1 Introduction 365 7.2 Construction 366 7.3 Working Principle 368 7.4 Rotating Field 369 7.5 Synchronous Speed and Slip Speed 374 7.6 Rotor Frequency and Speed 376 7.7 Rotor Voltage and Rotor Reactance 378 7.8 Rotor Torque 380 7.9 Starting Torque 381 7.10 Running Torque 386 7.11 Relationship Between Torques 389 7.12 Equivalent Circuit 393 7.13 Power Relationships 400 7.14 Approximate Equivalent Circuit 404 7.15 Condition for Maximum Mechanical Power 405 7.16 Power Stages 410 7.17 Torque-Slip Characteristics 413 7.18 Linear Induction Motor 415 7.19 Classification of Induction Motor by Properties 419 Exercise Problems 420 8 Starting and Control of an Induction Motor 423 8.1 Introduction 423 8.2 Direct Starting 423 8.3 Variable Resistance Starter 426 8.4 Autotransformer Starter 427 8.5 Star-Delta Starter 430 8.6 Simple Magnetic Starter 434 8.7 Forward-Reverse Starter 437 8.8 Cogging and Crawling 441 8.9 Importance of Deep Bar and Double Cage Rotor 442 8.10 Double Squirrel Cage Motor 445 8.11 Determination of Equivalent Circuit Parameters 449 8.12 Speed Control of Induction Motor 456 8.13 Automatic Star-Delta Starter 461 Exercise Problems 463 9 Synchronous Generator 465 9.1 Introduction 465 9.2 Construction 466 9.3 Pole and Frequency 469 9.4 Working Principle 471 9.5 Full-Pitch and Short-Pitch Windings 473 9.6 Pitch or Chording Factor 476 9.7 Distribution Factor 481 9.8 Effect of Harmonics on Pitch and Distribution Factors 484 9.9 EMF Equation of an Alternator 486 9.10 Equivalent Circuit of Synchronous Generator 494 9.11 Phasor Diagrams 496 9.12 Voltage Regulation 500 9.13 Tests of a Synchronous Generator 501 9.14 Power and Torque Expressions 507 9.15 Salient Pole Synchronous Generator 513 9.16 Power of a Salient Pole Generator 517 9.17 Parallel Operation of an Alternator 526 9.18 Load Sharing of Alternators 530 9.19 Synchronization of Alternators 532 9.20 Capability Curve of Alternators 535 Exercise Problems 539 10 Synchronous Motor 543 10.1 Introduction 543 10.2 Construction 543 10.3 Working Principle 544 10.4 Starting of Synchronous Motor 546 10.5 Equivalent Circuit 548 10.6 Phasor Diagrams 549 10.7 Synchronous Impedance Diagrams 552 10.8 Effect of Different Field Excitations 553 10.9 Power of Cylindrical Rotor 560 10.10 Various Conditions of Power 566 10.11 Phasor Diagrams of Salient Pole Motor 576 10.12 Power Expression of Salient Pole Motor 583 10.13 V-Curves of a Synchronous Motor 588 10.14 Power Factor Correction 591 10.15 Hunting of a Synchronous Motor 599 10.16 Applications of Synchronous Motor 600 10.17 Comparison of Synchronous Motor and Induction Motor 600 Exercise Problems 601 11 Single-Phase Induction Motors 603 11.1 Introduction 603 11.2 Construction and Synchronous Speed 603 11.3 Double Revolving Field Theory 605 11.4 Working Principle 607 11.5 Slip 609 11.6 Equivalent Circuit 611 11.7 Classification of a Single-Phase Motor 617 11.8 Starting of Single-Phase Motors 617 11.9 AC Series Motor 631 11.10 Reluctance and Hysteresis Motors 638 11.11 Test of a Single-Phase Motor 644 11.12 Stepper Motor 650 11.13 Step Angle of Stepper Motor 652 11.14 Permanent Magnet Stepper Motor 654 11.15 Variable-Reluctance Stepper Motor 657 11.16 Hybrid Stepper Motor 663 Exercise Problems 665 References 667 Index 669